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Subject[patch 40/71] sched: fix nr_uninterruptible accounting of frozen tasks really
2.6.30-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Thomas Gleixner <tglx@linutronix.de>

commit 6301cb95c119ebf324bb96ee226fa9ddffad80a7 upstream.

commit e3c8ca8336 (sched: do not count frozen tasks toward load) broke
the nr_uninterruptible accounting on freeze/thaw. On freeze the task
is excluded from accounting with a check for (task->flags &
PF_FROZEN), but that flag is cleared before the task is thawed. So
while we prevent that the task with state TASK_UNINTERRUPTIBLE
is accounted to nr_uninterruptible on freeze we decrement
nr_uninterruptible on thaw.

Use a separate flag which is handled by the freezing task itself. Set
it before calling the scheduler with TASK_UNINTERRUPTIBLE state and
clear it after we return from frozen state.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
include/linux/sched.h | 3 ++-
kernel/freezer.c | 7 +++++++
2 files changed, 9 insertions(+), 1 deletion(-)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -206,7 +206,7 @@ extern unsigned long long time_sync_thre
((task->state & (__TASK_STOPPED | __TASK_TRACED)) != 0)
#define task_contributes_to_load(task) \
((task->state & TASK_UNINTERRUPTIBLE) != 0 && \
- (task->flags & PF_FROZEN) == 0)
+ (task->flags & PF_FREEZING) == 0)

#define __set_task_state(tsk, state_value) \
do { (tsk)->state = (state_value); } while (0)
@@ -1630,6 +1630,7 @@ extern cputime_t task_gtime(struct task_
#define PF_MEMALLOC 0x00000800 /* Allocating memory */
#define PF_FLUSHER 0x00001000 /* responsible for disk writeback */
#define PF_USED_MATH 0x00002000 /* if unset the fpu must be initialized before use */
+#define PF_FREEZING 0x00004000 /* freeze in progress. do not account to load */
#define PF_NOFREEZE 0x00008000 /* this thread should not be frozen */
#define PF_FROZEN 0x00010000 /* frozen for system suspend */
#define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -44,12 +44,19 @@ void refrigerator(void)
recalc_sigpending(); /* We sent fake signal, clean it up */
spin_unlock_irq(&current->sighand->siglock);

+ /* prevent accounting of that task to load */
+ current->flags |= PF_FREEZING;
+
for (;;) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!frozen(current))
break;
schedule();
}
+
+ /* Remove the accounting blocker */
+ current->flags &= ~PF_FREEZING;
+
pr_debug("%s left refrigerator\n", current->comm);
__set_current_state(save);
}



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